1. Field of the Invention
The present invention relates to an exposure light-blocking film that is suitable for a multilayer interconnection structure in a semiconductor integrated circuit and can efficiently block exposure light (e.g., ultraviolet light) applied to a porous insulating film; to a material for forming an exposure light-blocking film, which is suitably used for the formation of the exposure light-blocking film; to a multilayer interconnection structure provided with the exposure light-blocking film and a manufacturing method thereof; and to a semiconductor device provided with the multilayer interconnection structure and a manufacturing method thereof.
2. Description of the Related Art
As the scale of integration of semiconductor integrated circuits and chip density have been increasing, so too has been, in particular, the demand for multilayered semiconductor chips. Against this background, the interval between adjacent interconnections, or interconnection interval, has become smaller and smaller, leading to a problem of interconnection delay due to an increased capacity between interconnections. Here, the interconnection delay (T) is represented by the equation T∝RC, which means that (T) is influenced by the interconnection resistance (R) and the capacity between adjacent interconnections (C). The relationship between permittivity (ε) and capacity (C) is represented by the equation C=ε0εr ·S/d (where S is an electrode area, ε0 is the permittivity of vacuum, εr is the permittivity of an insulating film, and d is the interconnection interval). The reduction of the capacity (C) can be achieved by reducing the interconnection thickness and the electrode area, though, reducing the interconnection thickness causes an increase in the interconnection resistance (R), making it impossible to achieve a speedup. Accordingly, reducing the permittivity of an insulating film is an effective way to achieve a speedup by minimizing the interconnection delay (T).
In a semiconductor device with a multilayer interconnection structure the interval between adjacent interconnections has become smaller and smaller with the recent trend moving toward an increased scale of integration of semiconductor integrated circuits and greater chip density, leading to an increased impedance of metal interconnections due to electrostatic induction. For this reason, there is a great concern that the response speed will be reduced and power consumption will be increased. To avoid this problem, it is necessary to reduce the permittivity of an interlayer insulating film as small as possible, which is provided between the semiconductor substrate and metal interconnections or between interconnection layers.
Materials for conventional insulating films include inorganic materials such as silicon dioxide (SiO2), silicon nitride (SiN) and phosphosilicate glass (PSG), and organic materials such as polyimides. The CVD-SiO2 film, an insulating film frequently used in semiconductor devices, however, has a permittivity of as high as 4. In addition, the SiOF film, an insulating film explored as a candidate for a low-permittivity CVD film, has a permittivity of as small as 3.3 to 3.5, but highly hygroscopic; therefore, the SiOF film has a problem that the permittivity increases with time. Moreover, a porous silica-based low-permittivity film has been proposed (see Japanese Patent Application Laid-Open (JP-A) No. 2004-153147). Since the production process for this porous film involves a pore formation step in which thermally decomposable components are heated, and evaporated or decomposed to form pores, it is possible to further reduce the permittivity of the porous film. At present, the pore size of this porous film, however, is large—10 nm or more. For this reason, increasing the porosity for reduced permittivity leads to a problem of increased permittivity and/or reduced film strength, caused due to moisture absorption.
At present, the following method has been explored to solve this kind of problem: After the deposition of an insulating film, the insulating film is cured by irradiation with ultraviolet light, plasmas, electron beams or the like to increase its film strength. However, ultraviolet light and plasmas unfavorably reach other films provided below the insulating film which is to be irradiated with them (or an exposure target). Thus, there is a concern about the use of ultraviolet light and plasmas because the thickness of lower interlayer insulating films may be reduced as a result of repeated curing operations. Moreover, there is a concern about the use of electron beams because their exposure energy is particularly high enough to undesirably damage transistors present in the lowermost layer.
It is an object of the present invention to solve the foregoing problems and to achieve the object described below.
More specifically, it is an object of the present invention to provide an exposure light-blocking film which has a high exposure light (particularly ultraviolet light) absorptivity, which efficiently blocks the exposure light that reaches porous insulating films present below an exposure target, and which is capable of reducing the permittivities of the porous insulating films without impairing their functions; a material for forming an exposure light-blocking film, which is suitably used for the formation of the exposure light-blocking film; a multilayer interconnection structure in which the parasitic capacity between adjacent interconnections can be reduced and an efficient mass-production method for the same; and a high-speed, highly-reliable semiconductor device provided with the multilayer interconnection structure and a manufacturing method thereof.